ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faultsgrafted

When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set,
a user fault may trigger show_pte() without any lock.
If another thread in the same process concurrently calls munmap(),
the page table pages may be freed while show_pte() is still traversing
them, causing a use-after-free in show_pte().

If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table
of PMD are freed when show_pte() is running.

Acquire mmap_write_lock() around show_pte() for user faults to fix the
contention.

For user faults, additionally restrict that show_pte() is called only
when the addr is a user-space address (addr < TASK_SIZE). This is because
the lock of tsk->mm only protects the virtual memory of user address space,
furthermore, dumping the page tables of a kernel-space address for user
faults is unnecessary and may have security implications.

Keep everything unchanged for kernel faults, because the kernel is
already in the "oops" state, acquiring a lock may risk a deadlock.

Co-developed-by: Qi Xi <xiqi2@huawei.com>

Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults")
Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com
Acked-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Signed-off-by: Qi Xi <xiqi2@huawei.com>
Signed-off-by: Xie Yuanbin <xieyuanbin1@huawei.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

1 files changed, 43 insertions, 0 deletions

diff --git a/drivers/char/Makefile b/drivers/char/Makefile
new file mode 100644
index 000000000..a46d7bf7c
--- /dev/null
+++ b/drivers/char/Makefile
@@ -0,0 +1,43 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Makefile for the kernel character device drivers.
+#
+
+obj-y				+= mem.o random.o
+obj-$(CONFIG_TTY_PRINTK)	+= ttyprintk.o
+obj-y				+= misc.o
+obj-$(CONFIG_TEST_MISC_MINOR)	+= misc_minor_kunit.o
+obj-$(CONFIG_ATARI_DSP56K)	+= dsp56k.o
+obj-$(CONFIG_VIRTIO_CONSOLE)	+= virtio_console.o
+obj-$(CONFIG_UV_MMTIMER)	+= uv_mmtimer.o
+obj-$(CONFIG_IBM_BSR)		+= bsr.o
+
+obj-$(CONFIG_PRINTER)		+= lp.o
+
+obj-$(CONFIG_APM_EMULATION)	+= apm-emulation.o
+
+obj-$(CONFIG_SONYPI)		+= sonypi.o
+obj-$(CONFIG_HPET)		+= hpet.o
+obj-$(CONFIG_XILINX_HWICAP)	+= xilinx_hwicap/
+obj-$(CONFIG_NVRAM)		+= nvram.o
+obj-$(CONFIG_TOSHIBA)		+= toshiba.o
+obj-$(CONFIG_DS1620)		+= ds1620.o
+obj-$(CONFIG_HW_RANDOM)		+= hw_random/
+obj-$(CONFIG_PPDEV)		+= ppdev.o
+obj-$(CONFIG_NWBUTTON)		+= nwbutton.o
+obj-$(CONFIG_NWFLASH)		+= nwflash.o
+obj-$(CONFIG_SCx200_GPIO)	+= scx200_gpio.o
+obj-$(CONFIG_PC8736x_GPIO)	+= pc8736x_gpio.o
+obj-$(CONFIG_NSC_GPIO)		+= nsc_gpio.o
+obj-$(CONFIG_TELCLOCK)		+= tlclk.o
+
+obj-y				+= agp/
+
+obj-$(CONFIG_HANGCHECK_TIMER)	+= hangcheck-timer.o
+obj-$(CONFIG_TCG_TPM)		+= tpm/
+
+obj-$(CONFIG_PS3_FLASH)		+= ps3flash.o
+
+obj-$(CONFIG_XILLYBUS_CLASS)	+= xillybus/
+obj-$(CONFIG_POWERNV_OP_PANEL)	+= powernv-op-panel.o
+obj-$(CONFIG_ADI)		+= adi.o